The present invention relates to a structure and components for a trailer coupler that attaches to the hitch ball of a towing vehicle. The structure and components are particularly suited to the gooseneck variety of trailer couplers but may also be used in other varieties of couplers. Gooseneck couplers typically extend downwardly from a nose of the trailer and provide a socket to receive a hitch ball. Such couplers typically include at a lowermost position a locking plate having a hole that can be aligned with the socket to receive the hitch ball, and misaligned so as to retain the hitch ball in the socket